As the chromosomes are in pairs, the corresponding genes also appear in pair. In normal persons, both the genes of a particular pair (chromosome no 11 and 16) are normal, i.e. they carry the message for synthesis normal hemoglobin. But in some persons, one of them may be normal and the other Thalassaemic. This person is said to be a carrier or Thalassaemia minor (trait). The carrier person may be either male or female and if a union takes place between two such carriers, there is a chance of 50% that their off springs will be carriers.

Thalassaemia Minor (Trait)
All children must inherit normal gene from the “normal” parents. However, they may inherit a normal or a Thalasaaemic gene. There is a one in two (50%) chance of inheriting the Thalassaemic gene from the carrier parent.

If this happens the child will be Thalasaaemia minor (trait). There is also a one in two (50%) chance of inheriting the normal gene from the carrier parent, if the latter happens the child will be completely normal. None of this compels the child to be Thalassaemia major.

Thalasaaemia Major
If both parents are carriers, when the mother produces an egg (once a month) the egg is either completely normal or completely Thalassemic. There is no way of telling in which order they will come. And when the father produces sperm, half are completely normal and half are Thalassaemic.

When the mother produces a normal egg, it does not matter what kind of sperm fertilizes it. If the sperm is normal, the child will be completely normal. If the normal egg meets a Thalassaemic sperm, the child will be carrier.

But if the mother produces a Thalassaemic egg, it matters a lot what kind of sperm meets it. If the sperm is normal, the child will be carier of Thalassaemia. But if the Thalassaemia egg is fertilized by a Thalassaemia sperm, the child will be Thalassaemia major. The carrier couples have a one in four (25%) chance that the child will inherit a normal gene from both parents, and so will be completely normal.

Detection of Thalassaemia
Diagnosis of Thalassaemia exploits certain characteristic abnormalities of the blood cells. These tests are very useful in detecting the carrier state which plays a major role in the prevention of Thalassaemia. A number of methods are utilized some of which are cheap and some expensive but which are more specific and sensitive.

Prevention of Thalassaemia
The best way of preventing the occurrence of the disease is to find out before marriage whether both the partners are carries or not. This can be done by performing a simple blood test, and if both the partners are found to be carriers, then such marriages should be discouraged or the partners may be persuaded not to bear any child. Diagnosis is also possible during antenatal period which allows a choice for medical termination of pregnancy.